论文标题

实验量子退火中的搜索范围

Search range in experimental quantum annealing

论文作者

Chancellor, Nicholas, Kendon, Viv

论文摘要

我们构建了一个具有工程能量景观的伊辛·哈密顿(Ising Hamiltonian),使其具有接近真正的全球最低解决方案的局部能量最小值,并远离错误的最低限度。使用先前实验中建立的技术,我们设计了实验,使得(至少在与我们的研究相关的时间尺度上)由于高量子波动的高水平而在正向退火时优先达到假最小值。这使我们能够证明反向退火的关键原理,即使在存在错误的最小值的情况下,也可以在本地搜索解决方案空间,优先找到附近的解决方案。据我们所知,这里使用的技术与以前使用的实验技术不同,并允许我们以先前尚未探索的方式探测设备的基本搜索范围。我们在两个通量量子量子退火器上执行这些实验,一个噪声水平高于另一个噪声水平。我们发现证据表明,较低的噪声设备更有可能找到最小的距离最小值(在这种情况下为错误的最小值),这表明降低噪声从根本上增加了磁通量量子量子退火器能够搜索的范围。我们的工作解释了为什么降低噪声会导致这些量子退火器的性能提高。这支持了这样一个想法,即这些设备可能能够快速搜索解决方案空间的广泛区域,这是量子退火器被视为具有量子计算优势的潜在途径的核心原因之一。

We construct an Ising Hamiltonian with an engineered energy landscape such that it has a local energy minimum which is near to the true global minimum solution, and further away from a false minimum. Using a technique established in previous experiments, we design our experiment such that (at least on timescales relevant to our study) the false minimum is reached preferentially in forward annealing due to high levels of quantum fluctuations. This allows us to demonstrate the key principle of reverse annealing, that the solution space can be searched locally, preferentially finding nearby solutions, even in the presence of a false minimum. The techniques used here are, to the best of our knowledge, distinct from previously used experimental techniques, and allow us to probe the fundamental search range of the device in a way which has not been previously explored. We perform these experiments on two flux qubit quantum annealers, one with higher noise levels than the other. We find evidence that the lower noise device is more likely to find the more distant energy minimum (the false minimum in this case), suggesting that reducing noise fundamentally increases the range over which flux qubit quantum annealers are able to search. Our work explains why reducing the noise leads to improved performance on these quantum annealers. This supports the idea that these devices may be able to search over broad regions of the solution space quickly, one of the core reasons why quantum annealers are viewed as a potential avenue for a quantum computational advantage.

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